Tools for tightening and binding strapping about packages and articles have been utilized for many years and they include pneumatic, hydraulic and electrically driven tools. Many of the earlier tools were utilized to cinch and secure steel strapping with clips, clamps, and formed interlocking notches. The introduction of plastic strapping required development of newer tools and new strap joining techniques, which included strap weldments. The tools for plastic strapping are most frequently pneumatically or electrically driven for both cost and weight considerations. The plastic strapping is constricted about a package by means of a mechanism which drives one end of overlapped strap portions so as to tighten the loop to a predetermined and sensed tensile load. Thereafter, the strap is held in position, the driving mechanism is disabled and the overlapped strap ends are secured together by means of fusion welding.
The tools for binding and securing plastic strapping are relatively new and require special techniques so as to provide sound weld joints for the overlapping strap ends forming the loop about a package. Weldments avoid the use of secondary clips and fasteners to join the taut strapping looped about bundles and packages. Indicative of the early efforts at hand tools for securing looped plastic strapping is the electrically controlled hand tool taught in U.S. Pat. No. 3,586,572 to Ericsson, which utilized a drive means coupled to an electric motor for tensioning the plastic strap looped about a bundle or package. Thereafter, the frictionally engaged and overlapping strap portions were rapidly oscillated so as to melt a surface region of the strapping for fusion by means of interface solidification so as to provide a weldment between the looped straps. The drive means included a rotary output shaft whose rotary motion was converted into a rocking movement for intermittent rotary movement of the strap gripping member so as to provide an oscillating movement for effecting the friction-fusion joining of the overlapping strap portions.
Earlier efforts at strap fusion and welding utilizing pneumatically operated tools is exemplified by the completely automatic-type application tool taught in U.S. Pat. No. 3,442,203-Kobiella, where plastic strap is automatically fed around a package from a strap supply source; the leading end of the strap is grasped; the trailing end of the strap is drawn backwardly so as to tension the strap loop; and, thereafter, the overlapping portions of the loop are friction fused. However, this apparatus is a stand-alone machine and not a completely portable hand-held tool.
Hand-held, pneumatically-operated tools have been provided so as to accomplish joining and fusion bonding or securing together plastic strapping. In these hand-held tools, the strap is manually fed about a package so as to bring the strapping portions into overlapping registry with respect to each other, the strap loop is tightly cinched and the strap ends are secured by means of friction-fusion. Indicative of these tools are the VFL and VFM tension-weld strapping tools provided by the Signode Corporation and illustrated as catalog number 186096, where overlapping strap portions are inserted into a feedwheel mechanism and an air motor is activated by means of a lever operator so as to tighten the strap about a package to a predetermined tension noted by means of the motor stalling. Thereafter, an eccentric handle is utilized to actuate the fusion operation. However, it has been found that the actuation time for the fusion operation will vary with the type of plastic, strap thickness, strap width, and ambient temperature, as well as operator ability to judge completion of the weldment.
Pneumatically operated tools have found wide application and usage within the strap industry as well as other industries. The manufacturers and suppliers of these tools have provided control mechanisms for controlling or sensing operations based upon their own initiative and in response to customer demand. In the strapping tool industry, tools are provided with means for sensing the strap tension and disengaging the drive mechanism at a predetermined strap tensile force, as well as other sophisticated controls which minimize operator judgment in providing a bound strap about a package. However, the tool manufacturers have not yet provided a means to minimize operator judgment with respect to the time function so as to provide a secure weldment between the overlapped plastic straps. Therefore, a device for controlling the fusion welding operation by means of these hand-held tools is very desirable so as to cure variations in the weldments, which are now dependent upon operator judgment. Although a timing control program or procedure in some form was previously conceivable, the desired device was required to be compact and easily adapted to existing friction fusion hand tools.